| 摘要 |
<p>A method of obtaining an NMR spectrum from a first region lying wholly within a second region of a sample material, comprises obtaining a signal indicative of a first NMR spectrum from substantially all of the second region of the sample material applying to the sample a magnetic field gradient, and simultaneously applying to the sample an Rf perturbing pulse having an amplitude and a frequency distribution such as to perturb nuclear spins in the said first region, but not outside it, removing the magnetic field gradient, and thereafter obtaining from the sample a signal indicative of a second NMR spectrum before relaxation of the perturbed spins in the said first region, and comparing the said first and second signals to obtain a difference spectrum attributable to the said region. Three separate perturbing pulses are preferably employed, each in the presence of a corresponding field gradient. The experiment is preferably repeated a large number of times, with the Rf carrier frequency stepped between each Rf pulse (for example every 500 microseconds).</p> |
